The purpose of this proposal is to determine how cardiac vagal and sympathetic cafferent inputs interact on neurons in the medullary reticular formation. The reticular formation is involved in the regulation of blood pressure, and it can influence heart rate and cardiac contractile force. Output functions of the reticular formation influence on sympathetic efferent nerve activity have been examined. Regarding input to the reticular formation, work has been limited to baroreceptor afferents. This proposal will be recorded extracellularly with metal microelectrodes. The effects on cell activity of noxious and innocuous stimuli applied to the heart will be studied. Noxious stimuli will include intracardiac injection of bradykinin and coronary artery occlusion. Innocuous stimuli will include aortic occulusion and infusion of dobutamine, a agonist. The effects on cell activity of these stimuli will be studied with (1) only sympathetic afferent fibers intact, (2) only cardiac vagal afferent fibers intact, and (3) with both pathways intact. Previous work has indicated that alterations in sympathetic and parasympathetic activity can produce deleterious cardiac arrhythmias, and facilitate the development of arrhythmias follwing myocardial infarction. Central mechanisms whereby autonomic activity would be changed have not been studied. The examination of cardiac vagal and sympatheti afferent interactions in the reticular formation will contribute to the understanding of central mechanisms underlying cardiac arrhythmias.